2,529 research outputs found
Gravitational cubic interactions for a massive mixed symmetry gauge field
In a recent paper arXiv:1107.1872 cubic gravitational interactions for a
massless mixed symmetry field in AdS space have been constructed. In the
current paper we extend these results to the case of massive field. We work in
a Fradkin-Vasiliev approach and use frame-like gauge invariant description for
massive field which works in (A)dS spaces with arbitrary values of cosmological
constant including flat Minkowski space. In this, massless limit in AdS space
coincides with the results of arXiv:1107.1872 while we show that it is
impossible to switch on gravitational interaction for massless field in dS
space.Comment: 13 page
First Order Actions and Duality
We consider some aspects of classical S-duality transformations in first
order actions taken into account the general covariance of the Dirac algorithm
and the transformation properties of the Dirac bracket. By classical S-Duality
transformations we mean a field redefinition that interchanges the equations of
motion and its associated Bianchi identities. By working from a first order
variational principle and performing the corresponding Dirac analysis we find
that the standard electro-magnetic duality can be reformulated as a canonical
local transformation. The reduction from this phase space to the original phase
space variables coincides with the well known result about duality as a
canonical non local transformation. We have also applied our ideas to the
bosonic string. These Dualities are not canonical transformations for the Dirac
bracket and relate actions with different kinetic terms in the reduced space.Comment: accepted for publication in IJMP
Spitzer Infrared Spectrograph Detection of Molecular Hydrogen Rotational Emission towards Translucent Clouds
Using the Infrared Spectrograph on board the Spitzer Space Telescope, we have detected emission in the S(0), S(1), and S(2) pure-rotational (v = 0-0) transitions of molecular hydrogen (H_2) toward six positions in two translucent high Galactic latitude clouds, DCld 300.2–16.9 and LDN 1780. The detection of these lines raises important questions regarding the physical conditions inside low-extinction clouds that are far from ultraviolet radiation sources. The ratio between the S(2) flux and the flux from polycyclic aromatic hydrocarbons (PAHs) at 7.9 μm averages 0.007 for these six positions. This is a factor of about four higher than the same ratio measured toward the central regions of non-active Galaxies in the Spitzer Infrared Nearby Galaxies Survey. Thus, the environment of these translucent clouds is more efficient at producing rotationally excited H_2 per PAH-exciting photon than the disks of entire galaxies. Excitation analysis finds that the S(1) and S(2) emitting regions are warm (T ≳ 300 K), but comprise no more than 2% of the gas mass. We find that UV photons cannot be the sole source of excitation in these regions and suggest mechanical heating via shocks or turbulent dissipation as the dominant cause of the emission. The clouds are located on the outskirts of the Scorpius-Centaurus OB association and may be dissipating recent bursts of mechanical energy input from supernova explosions. We suggest that pockets of warm gas in diffuse or translucent clouds, integrated over the disks of galaxies, may represent a major source of all non-active galaxy H_2 emission
On Dual Formulation of Gravity
In this paper we consider a possibility to construct dual formulation of
gravity where the main dynamical field is the Lorentz connection
\omega_\mu^{ab} and not that of tetrad e_\mu^a or metric g_\mu\nu. Our approach
is based on the usual dualization procedure which uses first order parent
Lagrangians but in (Anti) de Sitter space and not in the flat Minkowski one. It
turns out that in d=3 dimensions such dual formulation is related with the so
called exotic parity-violating interactions for massless spin-2 particles.Comment: 7 pages, plain LaTe
The Galactic dust as a foreground to Cosmic Microwave Background maps
We present results obtained with the PRONAOS balloon-borne experiment on
interstellar dust. In particular, the submillimeter / millimeter spectral index
is found to vary between roughly 1 and 2.5 on small scales (3.5' resolution).
This could have implications for component separation in Cosmic Microwave
Background maps.Comment: 4 pages, 1 figure, proceeding of the Multi-Wavelength Cosmology
conference held in Mykonos, Greece, June 2003, ed. Kluwe
The Spitzer Space Telescope First-Look Survey: Neutral Hydrogen Emission
The Spitzer Space Telescope (formerly SIRTF) extragalactic First-Look Survey
covered about 5 square degrees centered on J2000 17:18 +59:30 in order to
characterize the infrared sky with high sensitivity. We used the 100-m Green
Bank Telescope to image the 21cm Galactic HI emission over a 3x3 degree field
covering this position with an effective angular resolution of 9.8 arcmin and a
velocity resolution of 0.62 km/s. In the central square degree of the image the
average column density is N(HI) = 2.5 x 10^{20} cm-2 with an rms fluctuation of
0.3 x 10^{20}. The Galactic HI in this region has a very interesting structure.
There is a high-velocity cloud, several intermediate-velocity clouds (one of
which is probably part of the Draco nebula), and narrow-line low velocity
filaments. The HI emission shows a strong and detailed correlation with dust.
Except for the high-velocity cloud, all features in the HI map have
counterparts in an E(B-V) map derived from infrared data. Relatively high
E(B-V)/N(HI) ratios in some directions suggest the presence of molecular gas.
The best diagnostic of such regions is the peak HI line brightness temperature,
not the total N(HI): directions where Tb > 12 K have E(B-V)/N(HI) significantly
above the average value. The data corrected for stray radiation have been
released via the Web.Comment: Accepted for publication in the Astronomical Journal, April 2005. 25
pages includes 11 figures. The data and higher resolution figures are
available from http::/www.cv.nrao.edu/fls_gb
Response of Two Dams in the 1987 Whittier Narrows Earthquake
The 1987 Whittier Narrows earthquake (ML = 5.9) shook two dams, the Puddingstone and Cogswell dams, which were instrumented as part of the California Strong Motion Instrumentation Program (CSMIP). The resulting recorded accelerograms provided a valuable opportunity to investigate and evaluate the accuracy and reliability of conventional geotechnical procedures for evaluation of dynamic response characteristics of earth and rockfill dams. This paper presents the results of these studies, which provide insight regarding current techniques for dynamic soil property evaluation and the applicability of one- and two-dimensional analytical procedures to evaluation of the dynamic response of these types of dams
Comprehensive analysis of high-performance computing methods for filtered back-projection
This paper provides an extensive runtime, accuracy, and noise analysis of Computed To-mography (CT) reconstruction algorithms using various High-Performance Computing (HPC) frameworks such as: "conventional" multi-core, multi threaded CPUs, Compute Unified Device Architecture (CUDA), and DirectX or OpenGL graphics pipeline programming. The proposed algorithms exploit various built-in hardwired features of GPUs such as rasterization and texture filtering. We compare implementations of the Filtered Back-Projection (FBP) algorithm with fan-beam geometry for all frameworks. The accuracy of the reconstruction is validated using an ACR-accredited phantom, with the raw attenuation data acquired by a clinical CT scanner. Our analysis shows that a single GPU can run a FBP reconstruction 23 time faster than a 64-core multi-threaded CPU machine for an image of 1024 X 1024. Moreover, directly programming the graphics pipeline using DirectX or OpenGL can further increases the performance compared to a CUDA implementation
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